You talk of a 23,000 axle registerd at 21,000.
I’m guessing that your door jamb says 12,000 front and 21,000 rear.
And I’d guess you plate at 33,000 lbs.
I understand what you’re saying about the 12,000/13,200 axle.
If you want or need a 13,200 axle, just buy a 13,200 axle.
I’ve known...